This invention relates to the field of electrical signal separating devices or isolating and matching devices which are utilized to enable a heating element means of an electrically heatable window, i.e., a motor vehicle heated rear window (defroster) unit not designed specifically to be an antenna or aerial and essentially aperiodic and non-resonant at RF frequencies, to be used as an efficient radio frequency transmitting or receiving aerial, while the window unit is used simultaneously for a heating (demisting) purpose.
The electrical signal separating function of these devices is used for separating a radio signal from the heating element of an electrically heated window when the same is enabled to be used as a radio aerial.
Kropielnicki U.S. Pat. No. 4,086,594 discloses a device in the field of the present invention and provides an electrical signal separating device for separating a radio signal from the resistance heating element of an electrically heated window, and includes the usage of an isolating or blocking circuit which comprises a bifilar coil means arranged so as to provide high impedance paths for in-phase fluctuating currents but low resistance paths for currents flowing from a motor vehicle D.C. power supply, whereby the bifilar coil arrangement effectively blocks the radio frequency signals while passing the current from the D.C. power supply to the heating element, such referenced device being used to enable a heated rear window of a motor vehicle to be used as a receiving radio aerial and for heating purposes.
Another device in the field of the present invention is Kropielnicki U.S. application Ser. No. 359,304, filed Mar. 18, 1982, which will issue as U.S. Pat. No. 4,422,077 on Dec. 20, 1983, the disclosure of which provides an improvement of the above-referenced prior Kropielnicki U.S. patent.
Such improvement relates to enabling the use of a motor vehicle electrically heated window as a transmitting or receiving aerial at AM or VHF/FM wavelengths, and includes matching and tuning circuitry being operative to effectively match the impedance of the window heating element to an aerial feeder circuit of a transmitter so that efficient VHF transmission, from the motor vehicle electrically heated window of signals received at an aerial input terminal, is effected; this disclosed improvement further incorporating, in combination, isolating circuitry comprising a bifilar coil means.
The present invention provides further advantageous and improved embodiments in this field of invention and further provides specific improvements of the devices disclosed in the above-referenced U.S. patents, which improvements pertain, in particular, to improved isolating and/or matching circuitry embodiments which have significant advantages over the prior art recited hereinabove.